I wish economists would make that point more often and more loudly. DeLong kind of gets the low skilled manufacturing part in his post criticizing the consensus around globalization hurting wages. There's a lot of talk about how bargaining (read: unions) has been actively killed by Republicans the past 30 years or so, and a mention that low-skilled blue collar jobs aren't really great jobs, but since he's criticizing Larry Summers omissions I'm feel I should criticize his: there is no mention of service industry jobs.
This is a glaring omission for a couple reasons. One goes to the whole globalization issue: outsourcing service industry jobs is harder than manufacturing. Yes, you can locate a call center in India, but you can't really staff a grocery store for St. Louis residents by hiring people in Tanzania, or move goods within the US with truck drivers in China or go to get a physical from a doctor in Cuba. Those jobs don't globalize the way manufacturing can. They may also be harder to mechanize due to our preference for human contact/interactions.
The other reason it is an omission has to do with the reduction of bargaining power. The reason that manufacturing jobs are perceived as better is because they have, historically, paid better, and the reason for that is unions and bargaining. Low-skilled service jobs (operating a cash register, or stocking shelves) often do not have unions to support the wages and benefits. If Wal-Mart had ended up unionized when it was started I think the jobs in this country would be very different today. Now I don't think that the big box stores would be nearly as prevalent were that the case, and that's an alternate reality with far reaching consequences, but we perceive manufacturing as better than service, not because it is, but because it is associated with unions.